The use of high velocity, abrasive-laden liquid jets to precisely cut a variety of materials is well known. Briefly, a high velocity liquid jet is first formed by compressing the liquid to an operating pressure of 3,500 to 150,000 psi, and forcing the compressed liquid through an orifice having a diameter approximating that of a human hair; namely, 0.003–0.040 inches. The material defining the waterjet-forming orifice is typically a hard jewel such sapphire, ruby or diamond.
The resulting highly coherent jet is discharged from the orifice at a velocity which approaches or exceeds the speed of sound. The liquid most frequently used to from the jet is water, and the high velocity jet described hereinafter may accordingly be identified as a waterjet. Those skilled in the art will recognize, however, that numerous other liquids can be used without departing from the scope of the invention, and the recitation of the jet as comprising water should not be interpreted as a limitation.
To enhance the cutting power of the waterjet, abrasive materials have been added to the jet stream to produce an abrasive-laden waterjet, typically called an “abrasivejet”. The abrasivejet is used to effectively cut a wide variety of materials from exceptionally hard materials (such as tool steel, aluminum, cast iron armor plate, certain ceramics and bullet-proof glass) to soft materials (such as lead). Typical abrasive materials include garnet, silica, and aluminum oxide having grit sizes of #36 through #200.
To produce the abrasivejet, the waterjet passes through a “mixing region” wherein a quantity of abrasive is entrained into the jet by the low pressure region that surrounds the flowing liquid in accordance with the Bernoulli Principle. The abrasive, which is under atmospheric pressure in an external hopper, is drawn into the mixing region by the lower pressure region via a conduit that communicates with the interior of the hopper. In operation, quantities of up to 6 lbs./min of abrasive material have been found to produce a suitable abrasive jet.
The resulting abrasive-laden waterjet is then discharged against a workpiece through an abrasivejet nozzle that is supported closely adjacent the workpiece. The spent abrasive-laden water is drained away from the workpiece in any of a number of known ways, and collected in a collection tank for recycling of the abrasive and/or proper disposal.
During operation of abrasivejet systems, the fluid path between the mixing region and the discharge opening of the abrasivejet nozzle can become clogged or blocked sufficiently to cause the abrasive-laden water to back up to and into the external hopper. The system must then be shut down so that the external hopper can be emptied of the resulting slurry, cleaned, dried and refilled with abrasive. In addition, the abrasive-carrying conduit must be cleaned and dried or replaced, and the orifice member and other internal components of the cutting head must be cleaned as well. The resulting downtime of the cutting system increases the cost of production, adversely affects production schedules and creates unexpected messy work for the operator.